Movement detection/tracking systems (optical tracking systems or tracking systems) have numerous applications, including those detailed in the following patents; autonomous vehicles (U.S. Pat. No. 6,535,114), monitoring systems (U.S. Pat. No. 6,690,374), sports cameras (U.S. Pat. No. 6,567,038), conference video systems (U.S. Pat. No. 6,507,366), surgery (U.S. Pat. Nos. 6,725,079 and 6,662,036), positioning (U.S. Pat. No. 6,490,473), inspection (U.S. Pat. No. 6,259,960), spotlighting (U.S. Pat. No. 6,079,862), and machining (U.S. Pat. No. 6,429,404). Conventional tracking systems use one of several different types of sensors such as millimeter-wave, laser, ultrasonic wave, or infrared/visual imaging sensors. There are also numerous types of tracking apparatuses and signal processing schemes for use in conjunction with conventional tracking systems, including visual image tracking systems.
Conventional image tracking systems can be divided into two groups, single imaging systems and plural imaging systems. Single imaging systems (those having a single imaging camera) generally have a simpler configuration and image-processing scheme than plural imaging systems (those having multiple imaging cameras). However, single imaging systems cannot produce three-dimensional information. Furthermore, it is difficult to extract distance information from a single imaging system unless it is used in combination with a device such as a range finder. Additionally, because the field of view (FOV) of the imaging system is limited, it is easy to lose track of fast moving objects (that is, the single imaging systems typically have a high ‘tracking dropout’ rate).
FIGS. 1A-1B are block diagrams of prior art image tracking systems (tracking systems). In FIG. 1A, the image tracking system 100 includes an imaging camera (camera system) 101 configured to capture images. The imaging camera 101 may use either a visual or infrared wavelength. Imaging cameras using a visual wavelength may acquire a color image, but do not perform well at night or in heavy fog. Imaging cameras using an infrared wavelength cannot acquire a color image, but may be used at night or in heavy fog. Regardless of whether the imaging camera uses visual or infrared light, the construction of the imaging camera may be similar in its components.
An image sensor 102 is coupled to the imaging camera 101, configured to sense an image. The image sensor 102 may use either a visual or infrared wavelength. The image tracking system 100 also includes an image processor 103, communicatively coupled to the image sensor 102, configured to process the images sensed by the image sensor 102 and to generate an output signal 106. In the system, the image processor 103 may include an object-identifying algorithm.
In FIG. 1B, the prior art image tracking system 170 includes a tracking controller 104, communicatively coupled to the image processor 103. The image processor 103 is configured to generate image data 106 and position information of a tracked object and the tracking controller is configured to generate a tracking signal 108. In one embodiment, the tracking controller 104 includes a camera attitude control algorithm and attitude controller. A movement system 105 is mechanically coupled to the imaging camera 101 and communicatively coupled to the tracking controller 104, configured to adjust the attitude of the imaging camera 101 in response to the tracking signal 108 from the tracking controller 104. In one embodiment, the movement system 105 may include, for example, a servo or gimbal system.
Plural imaging systems are capable of generating three-dimensional information and reducing the dropout rate by using two lenses with different FOVs, one narrow FOV for high resolution image and one wide FOV for low tracking dropout rate. However, use of multiple imaging cameras in the plural imaging systems complicates the structure of the tracking system and its image-processing algorithm.
Image tracking systems typically require that the image of object being tracked be in the center of the image sensor, requiring a camera attitude control system. Typically, the attitude of the imaging camera is adjusted using a servo motor or a gimbal system.
U.S. Pat. No. 6,734,911 describes using a dual-angle lens to obtain both wide-angle imaging and narrow-angle imaging of a scene. However, the system described in the '911 patent uses a very complex lens and generates large image distortion for wide-angle imaging. Furthermore, this system requires that the attitude of the imaging camera be adjusted by a servo motor.
Therefore, what is needed is an optical tracking system offering a highly adjustable field of view with minimal distortion and simplified construction.